The catalyzed reaction of methanol and ammonia to produce the mono-, di-, and trimethylamines is well known in the art. Presently, the methylamines are produced commercially by a continuous process for methanol and ammonia using an amorphous silica-alumina catalyst. This continuous process yields an equilibrium controlled distribution of the methylamines.
U.S. Pat. No. 3,384,667 discloses a method for producing monosubstituted and disubstituted amines in preference to trisubstituted amines by reacting ammonia with an alcohol in the presence of a crystalline metal aluminosilicate catalyst having pores of a diameter that passed the monosubstituted and disubstituted amine products, but are too small to pass the trisubstituted amine product.
U.S. Pat. No. 4,082,805 discloses a process for the production of aliphatic amines by reaction of a C.sub.1 -C.sub.5 alcohol or ether with ammonia in the presence of a catalyst comprising a crystalline aluminosilicate having the structure of ZSM-5, ZSM-11 or ZSM-21, at 300.degree. to 500.degree. C. and at 1 atm to 1,000 psig pressure, the feed rate of alcohol or ether and ammonia being within the ratio of 1:1 to 5:1 g/hr.
U.S. Pat. No. 4,191,709 discloses a process for the manufacture of amines by reacting an alcohol with ammonia in the presence of the hydrogen form of zeolite FU-1 or zeolite FU-1 in which some or all of the protons have been replaced by bivalent or trivalent cations. The related U.S. Pat. No. 4,205,012 is similar except that the catalyst comprises zeolite FU-1 in which some or all of the protons have been replaced by monovalent cations, for example, sodium.
U.S. Pat. No. 4,229,374 discloses a process for producing tertiary amines by reacting alcohols with ammonia, primary amines or secondary amines in the presence of a specific catalyst. The catalyst comprises a mixture of copper, tin and an alkali metal supported on a suitable carrier, such as artificial and natural zeolites.
U.S. Pat. No. 4,254,061 discloses a process for producing monomethylamine by reacting methanol and ammonia, in such amounts so as to provide a C/N ratio, from the methanol and ammonia reactants, of 0.5-1.5, over a catalyst which is (a) mordenite wherein the primary cation is Li, Na, HNa having at least 2% Na by weight, K, Ca, Sr, Ba, Ce, Zn or Cr; (b) ferrierite wherein the primary metal cation is Li, Na, K, Ca, Sr, Ba, Ce or Fe; (c) erionite ore; (d) calcium erionite; or (e) clinoptilolite ore.
The methanol amination reaction is exothermic. Thus, in an adiabatic plug flow reactor for the production of methylamines, the temperature rises by about 150.degree.-400.degree. F. (83.degree.-222.degree. C.) depending on the ammonia:methanol feed ratio. The maximum allowable reactor temperature for methylamine is about 800.degree. F. (427.degree. C.), above which thermal reactions yielding coke and cracked by-products make the process inoperative.
The present silica-alumina catalysts require feed temperatures above 600.degree. F. (316.degree. C.) to obtain commercial methylamines production requirements. With a starting temperature of 600.degree. F. (316.degree. C.), the molar feed ratio of ammonia:methanol must be higher than 2 for the maximum temperature in an adiabatic reactor to be less than 800.degree. F. (427.degree. C.). Therefore, greater than two-fold excess ammonia over the stoichiometric requirement must be used to avoid coking and cracking. Use of such excess ammonia means large ammonia separation stills to recycle the ammonia.
Thus, improving the methanol conversion rate would offer advantages such as lower inlet temperatures permitting lower ammonia:methanol feed ratios and less excess ammonia to handle.